The present invention relates to a polarizable electrode for use in electrical double layer capacitors.
At present, uses of electrical double layer capacitors are being actively developed in various kinds of fields from the viewpoint of their sheet-like shape.
In particular, significant reduction in the usage of fossil fuels by cars is required from environmental and resource issues. As one of the measures for such reduction, the spotlight is on so-called hybrid cars, which achieve the reduction in fossil fuel usage by the combination of fossil fuel and electricity. In this field, higher output density is demanded of a high output density type of electrical double layer capacitors.
On the other hand, use has also increased for electrical double layer capacitors employed as so-called backup power sources in personal computers and various kinds of electrical machinery and apparatuses. In this field, although a high energy density type of electrical double layer capacitors has been used, higher energy density is demanded from the electrical double layer capacitors previously used.
For these reasons, with regard to the polarizable electrodes for use in the electrical double layer capacitors, it is essential to increase the density of carbon fine-powder in the polarizable electrodes.
However, in the polarizable electrodes currently used for electrical double layer capacitors, when the polarizable electrodes are impregnated with electrolytic solutions, the carbon particles contained in the polarizable electrodes are easily displaced therefrom. Therefore, there has been a problem of degradation in the performance of the electrical double layer capacitors.
Further, because the above polarizable electrodes have many particles suspended in the electrolytic solution, there has been a problem that energy losses in the electrical double layer capacitors becomes large due to high self-discharge therein.
The present invention has been achieved in view of the fact that the conventional technologies have such problems described above. Thus, an object of the present invention is to provide a polarizable electrode for use in electrical double layer capacitors which can reduce the long-term performance degradation and self-discharge caused energy losses of prior art electrical double layer capacitors. This is accomplished by suppressing the amount of carbon particles displaced from the polarizable electrode when the polarizable electrode is impregnated with an electrolytic solution.
According to the present invention, there is provided a polarizable electrode for use in electrical double layer capacitors. The polarizable electrode includes a carbon fine-powder, a conductive auxiliary agent, and a binder. The tensile strength of the above described polarizable electrode is not less than 0.13 MPa.
According to an aspect of the present invention, the amount of carbon particles displaced from the polarizable electrodes into an electrolytic solution in the double layer capacitor is preferably not more than 1.0 mg/cm2.